A number of devices for this purpose have already been proposed beside the well known simple conduit-draw-wire defined by a bendable element with the cross-sectional diameter of some millimeters and a length of several meters.
In Swiss Pat. No. 304 515, issued on Mar. 16, 1955 to Gesellschaft fur Kunsthornindustrie, an improved conduit-draw-wire is described which consists of a large number of rigid bead-shaped elements perforated with axial holes and threaded together by a bendable, not stretchable wire terminated at one end by a wire loop for hooking fast to a conductor, and at the other end either by an identical hook or by a bead element defining an end piece.
A single helical compression spring may be inserted between the loop and the adjacent first bead element to compensate possible undesired stretching of the wire, but otherwise the whole length of the wire is covered by closely adjacent bead elements. The bead elements may be elongate and have a spherical convex front face at one end and a funnel-shaped recess on the other end into which said front face of an adjacent element can be accommodated in order to achieve increased rigidity of the whole device.
In the Swedish Pat. No. 140 707 issued on Mar. 19, 1953 to A. Brunschweiler & Cie. an apparatus for pushing a conduit-draw-wire defined by a bendable bar of plastics material, into a conduit is described. The apparatus comprises two coaxial tubes, one telescoped into the other, and a third tube, aligned with and spaced from the other two tubes. A pushing mechanism for the draw wire, comprising a carrier element, is mounted between the two telescoped tubes and the third tube. This mechanism is stationary relative the tubes.
Another apparatus to facilitate the introduction of conductors into conduits is described in the U.S. Pat. No. 1,959,490 issued on May 22, 1934 to T. Mistelski. Here, no conduit-draw-wire is used, but the conductor itself is fed through a slotted or drilled bar accomodated in a rigid and possibly longitudinally slotted tube at the rear end of which an actuating mechanism for the rod is provided to reciprocatorily move it in said tube.